Japanese Patent No. 3975918 (Patent Literature 1) discloses an antenna device included in a mobile electronic apparatus for use in RFID systems.
As shown in FIG. 1A, an antenna device 70 of Patent Literature 1 includes an asymmetrical coil where two positions are opposed to each other with the center of the winding area of a coil 71 therebetween and the winding pitch varies between the two positions. On a side 71a having a larger winding pitch, a magnetic body 72a is disposed on the back of a main surface opposed to an IC card; on a side 71b having a smaller winding pitch, a magnetic body 71b is disposed on the main surface opposed to the IC card. As shown in FIG. 1B, the distribution of a magnetic field generated by the antenna device 70 is an asymmetrical distribution where the magnetic field is enhanced on the side 71a having a larger winding pitch and a larger line width of the loop coil 71. As shown in FIG. 1C, the antenna device 70 is disposed in a main body 91 of a communication terminal apparatus 90.